Acoustic device



c. KYLE 1,746,540

"ACOUSTIC DEVICE Feb. 11, 1930.'

Fyiled May 25, 1,927

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O O o 0 O o O 3 O O O O o o C? II O O O O O g g ,V7 n @'@Oo O O O O OOC2, OOM .2%. O O O O o oO G O `o o O @o y O INVEN TOR. Pfn/ d? PatentedFeb. ll, v1930 UNITED STATES PATENT OFFICE COLIN KYLE, OF SAN JOSE,CALIFORNIA, ASSIGNOR TO NEWCOMBEEIAWLEY, ING., 0F p CHICAGO, innmois, AConformation or DELAWAi-i 4.acotisrrc DEVICE Application filed May 251927. Serial'No. 194,010.

This invention relates to a condenser or electrostatic type of acousticdeviceand especially to a modified form of a device shown in myco-pending application entitled Acoustic device filed October 4, 1926,Ser. No. 139,-

rl`he device shown in the application re ferred to consists of a rigidperforated metallic plate, a thin, flexible metallic plate and anintermediate thin flexible dielectric diaphragm. An 4electric potential,when applied to the plates of the condenser,causes electrostaticattraction, which varies according to the degree of applied potential,and movement is thereby transmitted to the ilexible metallic plate andthe diaphragm which produces sound or acoustic vibrations in thesurrounding air coupled therewith. y 0

ll have .discovered that the dielectric diaphragm interposed between therigid perforated metallic plate and the thin, flexible metallic platemay be entirely eliminated .by substituting a soft, yielding buffermaterial. This substitution permits a closer spacing between theflexible and the rigid plate with corresponding increase in efficiency,and furthermore permits the flexible plate to serve `not only as thesecond plate of the condenser, but also as a diaphragm. I

The object of the present invention isvaccordingly that of generallyimproving and simplifying the construction and operation of acousticdevices of the condenser or electrostatic type, to provide a structurewhich permits a closer spacing between the plates of the condenser, toprovide a structure which permits the flexible plate to serve twofunctions: first, that of one of the plates of the condenser and second,that of a diaphragm, and further toprovide a perforated rigid plate inwhich perforations of varying diameter may be employed.

The invention is shown by Way of illustrations in the accompanyingdrawings in which:

Fig. 1 is a plan view of the condenser or electrostatic acoustic device.

Fig. 2 is a cross-section taken on line II-II, Fig. 1.

Fig. -3 is an enlarged cross-section of a portion of the device shown inFig. l.

Figs. 4 and 5 are enlarged cross-sections of acoustic devices of thecharacter described, showing modifications of the structure.

Referring to the drawings in detail, and particularly Figs. l, 2 and 3,A indicates a rigid perforated metallic plate which is provided with anannular rim 2. rlhe plate maybe constructed of practically any metal,for instance steel, iron, brass, copper, aluminum, etc., but it shouldbe sufficiently thick or heavy to prevent it from vibrating when the'acoustic device is being operated. The plate may have any exteriorcontour desired but it is in this instance shown as circular or discshaped in general formation. The surface presented is rounded orspherical and it serves as a support for a buffer material generallyindicated at B and a flexible metallic plate generally indicated at C.The buffer material is interposed between the rigid plate A and theflexible metallic plate C and a number of different buffer materials maybe employed, such as a coating of thin rubber, granulated rubber or thelike. In fact any material which has the quality of being comparativelysoft and resilient, and it may be a dielectric material, a partiallydielectric niaterial, and in some instances it may even be formed of amaterial having electric conducting qualities, as will hereinafterappear.

The flexible metallic plate C may consist of practically any material.For instance, any' of the metals which are capable of being rolled intoa thin leaf, such as gold leaf, silver leaf, etc., or it may consist ofany electric conducting material, whether metallic or otherwise, such asgraphite, sprayed metal, metal deposited by electrolytic action,plating, or of metal deposited by a solution such as chloride of gold,etc.

In one form of the invention, as actually constructed and used, anordinary perforated steel plate approximately of 16 gauge material isemployed, as illustrated at A in Figs. l, 2 and 3. This plate is cutcircular or otherwise and'provided with a rim 2. The main face ishammered or subjected to die action to produce a rounded or sphericalsurface. A thin coating of rubber is then aplied to the upper surface ofthe plate, as indicated at B, care being taken that no film is formedover `the perforations indicated at 3. The thin coating of rubber may bevulcanized and the surface treated with soapstone or the like, so as toproduce a resilient, soft, ieldin non-adhesive surface. After the pfateA ias been coated with rubber, as specified, it is ready for thereception of the metallic, flexible plate, indicated at C. This isprepared and applied in the following lmanner:

A piece of thin silk cloth, paper, or the like,

is spread out on a fiat surface and rubber cement is applied. Gold leafor like material is then placed on the surface and will adhere thereto,due to the application of the cement. When the cement is dried the clothor paper having the old leaf secured thereto is placed over the ru bercoated perforated plate A, as shown in Figs. 2 and 3, that is with thegold leaf in contact with the rubber coated surface of the plate. Thefabric, together with the gold leaf, is then preferably stretched to acertain degree and bent over the rim 2, and is then secured by afriction or clamping ring, such as indicated at 4. The device soconstructed is ready for use and may be connected with any receivingradio set, telephone circuit or the like, but preferably with atelephone or radio circuit, which has power amplification in the audiofrequency side of the circuit, the two terminals leading from the audiofrequency amplifying ower circuit being connected, one to the gold eafand one to the plate A. A modulated or varying current potential is inthis manner applied to the two plates and electrostatic attractionvarying according to the degree of ap lied potential will cause movementof the exible plate with relation to the rigid plate. The flexible plateaccordingly serves not only as a second plate of the condenser orelectrostatic device, but it also functions as a diaphragm, as it makesa direct couplin with the surrounding atmosphere and wil accordinglyconvert'the varying current potentials imposed on the plates into soundor acoustic vibrations. The fabric or paper to which the gold leaf issecured is indicated at D. It merely serves the function of a supportingmedium for the gold leaf; practically any supporting medium mayaccordingly be'employed, whether it be paper, silk or any other thin,flexible fabric, thin rubber sheeting or otherwise.

A modification is illustrated in Fig. 4, in this instance the perforatedplate A is covered with finely granulated rubber, or alike material.That is a material which has the qualities of being soft and resilientand preferably dielectric, the gold leaf and its supporting fabric beingapplied Vin the same manner as described in connection with Figs.

1, 2 and 3, the granulated buffer material emloyed in the modificationshown in Fig. 4 eing indicated at 6.

In Fig. 5 a form of the invention is illustrated which shows that it isnot absolutely essential to employ a buffer material which isdielectric. For instance, it has been found that any soft, yieldingbuffer material, for instance of a gelatinous character, may beemployed, a material similar to that used in printers ink rolls and thelike. This material is not exactly dielectic and it is accordinlynecessary to insulate the flexible plate, in icated at C, with relationthereto. A supporting material, such as a thin sheet of rubber or thelike, indicated at 7, must accordingly be employed. This is placed nextto the gelatinous buffer material indicated at 8, while the gold leaf,indicated at C, is applied to the exterior surface of the supportingmember 7.

It should be understood in all instances that while gold leaf has beenmore or less generally referred to, it is ossible to employ a flexiblemetallic plate, wlin'ch is applied to the supporting material byelectroplating, spraying, etc. In fact, any iiexble conductor may beemployed, whether metallic or otherwise.

By referring to Fig. l it will be noted that the perforations indicatedat 3 are of varying diameter, the innermost perforations indicated at 3being comparatively small and the outermost perforations comparativelylarge and the intermediate perforations being graduated in size. Thisprovision of perforations of varying diameter is of considerableimportance, as it has been found that tone vibrations of practically anyfrequency may be taken care of. The frequencies of audible tones rangeall the way from a few hundred'vibrations per second to as much as15,000 per second. The flexible plate C rests directly on the buffermaterial B, and as such forms a covering for the perforations. Thecovering extending over each of these perforations accordingly acts as adiaphragm and due to the fact that perforations of varying diameter areemployed, a multiplicity of diaphragms of varying diameter are alsoemployed. Actual experience has shown that a diaphragm of a givendiameter will reproduce tones of a certain frequency to practically 100per cent eiiiciency and that diaphragms of greater or less diameter willsimilarly reproduce tones having other frequencies. The general resultis faithful, clear, tone reproduction.

While the device is particularly intended for use as a loud speaker inconnection with radio sets, telephones, etc., it should be understoodthat it will also serve the function of a transmitter, this being moreor less selfevident to those familiar with the art.

What I claim and desire to secure by Let. ters Patent is:

1. A n acoustic device comprising a rlgid perforated metallic plate, asoft iiexible buffer material covering the unperforated portions of theplate only so as to leave the perforations uncovered and a liexibleelectric conductor supported by the buffer material.

2. acoustic device' comprising a rigid` lo perforated metallic plate, asoft yielding dielectric material forming a thin coating overtheunperforated portions of the lplate fonly so as to -leave theperforations uncovered and an electric conductor maintained in contactwith the buii'er material.

3. An acoustic device comprising a rigid metallic plate, said platehaving perforations formed therein of varying diameter, a flexibleelectric conducting Ymaterial forming a second plate and a dielectricmaterial interposed between the plates. u

4. An acoustic device comprising a rigid metallic plate, said platehaving perfora- .tions formed therein of varying dlameter,

a ilexible metallic plate coverinl the .perforated plate and a soft,flexible dielectric ma terial interposed between the platesl andcontacting with each ofthe plates. e

5. An acoustic device comprising a rigid l k perforated' metallic late,a flexible plate,

and a dielectric bu er material interposed between the flexible plateand the unperforated portions only of the rigid plate so as to leave theperforations uncovered by the buffermaterial.

6. An acoustic device comprising a rigid perforated metallic plate, asoft flexible buffer material secured to one face of the plate andcovering the unperforated portions of ofthe plate only so as to leavethe erforationsuncovered by the buffer materia and a flexible electricconductor maintained in lcontact with the buler material.

7. An acoustic device comprising a rigid perforated metallic late; abuier material securing the -unper orated ortion of the plate onl so asto leave t e perforations uncovere a flexible dielectric materialcovering the buffer and the perforated portions ate 5p of the plate anda flexible metallic p supported by th dielectric material. COLIN KYLE.

